The present invention is directed to solving a problem which occurs during the manufacture of shaped devices formed from aqueous collagen-containing dispersions. The present invention is particularly useful for forming shaped ophthalmic devices which retain a predetermined curvature. It is therefore imperative that there not be a memory imposed on the device during the manufacturing process which would distort the device into a configuration other than the predetermined desired shape. Although the process of the present invention is applicable to any shaped collagen-containing device, it is particularly useful for the formation of lenticular devices used for ophthalmologic treatment of trauma, post-surgical care, and for delivery of therapeutic agents to the eye. Such devices, in the shape of a thin lens, are usually biodegradable, hydrophilic and lubricous.
The material most commonly used for fabricating such devices is a high-purity collagen protein, such as those available from bovine corium or tendon.
Commonly used methods for producing such devices include film-forming methods, such as the casting of a collagen dispersion over a mold of a predetermined desired shape. A major problem in the production of such devices by these methods is the creation of residual stresses during drying which result in deformation from the cast shape upon rehydration of the device. Such deformation in the instance of a lenticular shape is usually manifested by a flattening or cone shape as opposed to the desired curved shape. The deformation can cause various problems during usage of the device on the eye, such as difficulty in placement, poor retention and discomfort.
Another major problem in manufacturing collagen-containing devices is associated with the drying period. Lenticular devices such as those described above may be dried over a period of several days using heat (at a relatively constant temperature) and high humidity. Under such conditions, microbial growth is a problem, leading to unacceptable products. It is desirable therefore to provide a method for drying collagen devices rapidly to minimize or eliminate microbial and endotoxin contamination.
It is therefore an object of the present invention to provide a method for rapidly drying devices formed from aqueous collagen-containing dispersions to minimize or to avoid microbial growth and endotoxin production.
It is another object of the present invention to provide a process for controlling the residual stresses in a casting operation to form films from aqueous collagen-containing dispersions.
It is yet another object of the present invention to provide a residual stress-free collagen ophthalmic device.
These objects and other objects may be provided by the following description and by practice of the invention.